In case where an air bag is provided for protecting an occupant sitting on a vehicle seat, an occupant determination device is provided at the vehicle seat for determining whether an occupant is seated or not on the corresponding seat, the occupant is an adult or a child, or the like. Japanese Patent Laid-open Publication No. 09-207638 discloses a known occupant determination device. The disclosed device includes a plurality of load sensors provided at a plurality of fixing positions respectively of a seat body facing a vehicle floor, and a controller for calculating a detection load value based on load values output from the plurality of load sensors and for determining whether or not an occupant is seated on the vehicle seat based on the calculated detection load value. More specifically, the controller calculates the detection load value by summing up the load values output from the plurality of load sensors using an adder, compares this detection load value with a load value set in advance (threshold value for determination) using a determination processing circuit, and determines whether or not an occupant is seated on the vehicle seat by comparing the detection load value and the threshold value for determination.
The vehicle seat on a passenger side may be equipped with a child restraint system (hereinafter referred to as “CRS”). In process of installing the CRS on the seat, a large load in downward direction is added to the seat by tightening the CRS with the seatbelt. At this time, a load greater than the original CRS's is detected, thereby possibly causing a wrong determination that an adult is sitting on the seat.
In order to prevent a wrong determination that an adult is sitting on the seat when installing the CRS on the seat, the installation of the CRS on the seat is desired to be determined. In Japanese Patent Laid-Open Publication No. 10-194076, it is disclosed that a predetermined communication is possible between the vehicle seat and the CRS. That is, the installation of the CRS on the seat can be determined by the communication function between the vehicle seat and the CRS.
In addition, Japanese Patent Laid-Open Publication No. 2001-187541 discloses a CRS determination based on a distribution status of pressure applied to the vehicle seat. Further, Japanese Patent Laid-Open Publication No. 2002-178813 discloses a CRS determination using the aforementioned detection load value instead of structures disclosed in Japanese Patent Laid Open Publication No. 10-194076 or No. 2001-187541. That is, the CRS is determined based on a load variation (variation of the detection load value) occurring when installing the CRS on the vehicle seat.
When the CRS is determined based on the load variation occurring when installing the CRS on the seat, a wrong determination may occur due to the load variation caused by a vibration under the vehicle running and the like.
Thus, a need exists for an occupant determination device that can determine accurately whether or not a child restraint system is equipped on the vehicle seat.